Absorbents that can absorb carbon dioxide have been used in various fields, for example, for concentration of carbon dioxide by PSA method and for absorption of carbon dioxide contained in the combustion exhaust gases from electric power plants. Examples of the carbon dioxide absorbents used for such purposes include activated carbon, various synthetic zeolites such as synthetic zeolite 13X, and the like.
For absorption of carbon dioxide, proposed was a zeolite-based carbon dioxide absorbent wherein 2 to 80 equivalent % of the cations thereof were replaced with Ba ions, which was prepared by immersing an zeolite in an aqueous solution containing a water-soluble Ba salt (see, for example, Patent Document 1). This material is a material suited for concentration and separation of carbon dioxide by PSA method and it is designed to have a larger ratio of carbon dioxide- to nitrogen-absorbing capacity. The zeolite used is, for example, a Na-A zeolite.
Alternatively as an absorbent for absorption of hydrocarbons in the exhaust gases from internal-combustion engines, proposed were zeolite-based hydrocarbon absorbents carrying at least one metal component selected from Ag, Cu, Ni, Zn, Ba, and Mg on the surface (see, for example, Patent Document 2). It is described that ZSM-5, mordenite, or Y zeolite carrying an Ag component at an ion exchange rate of 10% or more is particularly favorable for increase of desorption temperature.
Also proposed was a zeolite-based chlorine gas absorbent containing an alkali metal or alkali-earth metal (see, for example, Patent Document 3). In particular, it is an absorbent used for concentration and separation of chlorine gas by PSA method and, for example, Y or 13X zeolite ion-exchanged with Ca, Ba, or Li ions.